FIGS. 1 and 2 are schematic diagrams of two types of prior art vacuum plasma processors. The workpiece processor illustrated in FIG. 1 includes vacuum plasma processing chamber assembly 10, a first circuit 12 for driving a reactance for exciting ionizable gas in chamber assembly 10 to a plasma state, a second circuit 14 for applying RF bias to a workpiece holder in chamber assembly 10, and a controller arrangement 16 responsive to sensors for various parameters associated with chamber assembly 10 for deriving control signals for devices affecting the plasma in chamber assembly 10. Controller 16 includes microprocessor 20 which responds to various sensors associated with chamber assembly 10, as well as circuits 12 and 14, and signals from operator input 22, which can be in the form, for example, of a keyboard. Microprocessor 20 is coupled with memory system 24 including hard disk 26, random access memory (RAM) 28 and read only memory (ROM) 30. Microprocessor 20 responds to the various signals supplied to it to drive display 32, usually a typical computer monitor.
Hard disk 26 and ROM 30 store programs for controlling the operation of microprocessor 20 and preset data associated with different recipes for the processes performed in chamber assembly 10. The different recipes concern gas species and flow rates applied to chamber assembly 10 during different processes, the output power of AC sources included in circuits 12 and 14, the vacuum applied to the interior of chamber assembly 10, and initial values of variable reactances included in matching networks of circuits 12 and 14.
Plasma chamber assembly 10 includes chamber 40 having metal, non-magnetic cylindrical side wall 42 and metal, non-magnetic base 44, both of which are electrically grounded. Dielectric, typically quartz, window 46 is fixedly positioned on the top edge of wall 42. Wall 42, base 44 and window 46 are rigidly connected to each other by suitable gaskets to enable a vacuum to be established within the interior of chamber 40. Planar plasma excitation coil 48, for example, as configured in Ogle, U.S. Pat. No. 4,948,458 or Holland et al., U.S. Pat. No. 5,759,280, sits on or in very close proximity to the upper face of window 46. Coil 48, an electric reactance, reactively supplies magnetic and electric AC fields usually at an RF frequency, such as 13.56 MHz, to the interior of chamber 40, to excite ionizable gas in the chamber to a plasma, schematically illustrated in FIG. 1 by reference numeral 50. In other configurations, coil 48 is replaced with a powered or grounded electrode 55 that extends parallel to electrode 56, typically located in window 46 in close proximity to chamber 40 as illustrated in FIG. 2.
The upper face of base 44 carries holder, i.e. chuck, 52 for workpiece 54, which is typically a circular semiconductor wafer or a rectangular dielectric plate such as used in flat panel displays. Robotic arm 53 inside chamber 40 or coupled through a suitable air lab to the chamber interior responds to position control signals microprocessor 20 derives to correctly position workpiece 54 on chuck 52 so the center of the workpiece and chuck are vertically aligned. Microprocessor 20 derives the position control signals in response to position sensors (e.g., photodetectors) for sensing the relative positions of workpiece 54 and chuck 52. Chuck 52 typically includes metal plate 56 that forms an electrode (a reactive element). Electrode 56 carries dielectric layer 58 and sits on dielectric layer 60, which is carried by the upper face of base 44. Workpiece 54 is cooled by supplying helium from a suitable source 62 to the underside of dielectric layer 58 via conduit 64 and grooves (not shown) in electrode 56 and by supplying a liquid from a suitable source (not shown) to conduits (not shown) in chuck 52. With workpiece 54 in place on dielectric layer 58, DC source 66 supplies a suitable voltage through a switch (not shown) to electrode 56 to clamp, i.e., chuck, workpiece 54 to chuck 52. Chuck 52 can be monopolar or bipolar. When chuck 52 is bipolar, and designed for use with semiconductor wafers, electrode 56 includes two or more concentric, mutually-insulated circular metal elements having differing DC voltages applied to them.
With workpiece 54 secured in place on chuck 52, one or more ionizable gases from one or more sources 68 flow into the interior of chamber 40 through conduit 70 and port 72. For convenience, port 72 is shown as being in sidewall 42 but it is to be understood that gas usually is distributed by a manifold in the top of chamber 40. For convenience, only one gas source 68 is shown in FIG. 1, but it is to be understood that usually there are several gas sources of different species, e.g. etchants, such as SF6, CH4, C12 and HBr, dilutants such as Ar or He, and O2 as a passivation gas. The interior of conduit 70 includes valve 74 and flow rate gauge 76 for respectively controlling the flow rate of gas flowing through port 72 into chamber 40 and measuring the gas flow rate through port 72. Valve 74 responds to a signal microprocessor 20 derives, while gauge 76 supplies the microprocessor with an electric signal indicative of the gas flow rate in conduit 70. Memory system 24 stores for each recipe step of each workpiece 54 processed in chamber 40 a signal indicative of desired gas flow rate in conduit 70. Microprocessor 20 responds to the signal that memory system 24 stores for desired flow rate and the monitored flow rate signal gauge 76 derives to control valve 74 accordingly.
Vacuum pump 80, connected to port 82 in base 44 of chamber 40 by conduit 84, evacuates the interior of the chamber to a suitable pressure, typically in the range of one to one hundred millitorr. Pressure gauge 86, in the interior of chamber 40, supplies microprocessor 20 with a signal indicative of the vacuum pressure in chamber 40. Memory system 24 stores for each step of a particular workpiece processing recipe a signal indicative of desired vacuum pressure for the interior of chamber 40. Microprocessor 20 responds to the stored desired pressure signal memory system 24 derives for each recipe step and an electric signal from pressure gauge 86 to supply an electric signal to a drive for a gate valve (i.e. variable constriction) 87 in conduit 84 to maintain the pressure in chamber 40 at the set point or predetermined value for each recipe step.
Optical spectrometer 90 monitors the optical emission of plasma 50 by responding to optical energy emitted by the plasma and coupled to the spectrometer via window 92 in side wall 42. Spectrometer 90 responds to the optical energy emitted by plasma 50 to supply an electric signal to microprocessor 20. Microprocessor 20 responds to the signal that spectrometer 90 derives to detect an end point of the process (either etching or deposition) that plasma 50 is performing on workpiece 54. Microprocessor 20 responds to the signal spectrometer 90 derives and a signal memory system 24 stores indicative of a characteristic of the output of the spectrometer associated with an end point to supply the memory with an appropriate signal to indicate that the recipe step has been completed. Microprocessor 20 then responds to signals from memory system 24 to stop certain activities associated with the completed recipe step and initiate a new recipe step on the workpiece being processed in chamber 40 or commands release of workpiece 54 from chuck 52 and transfer of a new workpiece to the chuck, followed by instigation of another series of recipe processing steps.
Excitation circuit 12 for driving coil 48 includes constant frequency RF source 100, having a constant output power and typically having a frequency of 13.56 MHz. Source 100 drives power amplifier 102, having an electronically controlled power gain, so that the amplifier response time is on the order of a few microseconds or less, i.e., the output power of amplifier 102 changes from a first value to a second value in a few microseconds or less. The output power of amplifier 102 is in the range between 100 and 3000 watts. Amplifier 102 typically has a 50 ohm output impedance, all of which is resistive and none of which is reactive. Hence, the impedance seen looking back into the output terminals of amplifier 102 is typically represented by (50+j0) ohms, and cable 106 is chosen to have a characteristic impedance of 50 ohms.
For any particular recipe, memory system 24 stores a signal for desired output powers of amplifier 102. Memory system 24 supplies the desired output power of amplifier 102 to the amplifier by way of microprocessor 20. The output power of amplifier 102 can be controlled in an open loop manner in response to the signals stored in memory system 24 or control of the output power of amplifier 102 can be on a closed loop feedback basis. As the output power of amplifier 102 changes, the density of plasma 50 changes accordingly, as disclosed by Patrick et al., U.S. Pat. No. 6,174,450.
The output power of amplifier 102 drives coil 48 via cable 106 and matching network 108. Matching network 108, typically configured as a “T,” includes two series legs including variable capacitor 112 and fixed capacitor 116, as well as a shunt leg including variable capacitor 114. Coil 48 includes input and output terminals 122 and 124, respectively connected to one electrode of capacitor 112 and to a first electrode of series capacitor 126, having a grounded second electrode. The value of capacitor 126 is preferably selected as described in the commonly assigned, previously mentioned, Holland et al. patent.
Electric motors 118 and 120, preferably of the step type, respond to signals from microprocessor 20 to control the values of capacitors 112 and 114 to maintain an impedance match between the impedance seen by looking from the output terminals of amplifier 102 into cable 106 and by looking from cable 106 into the output terminals of amplifier 102. Hence, for the previously described (50+j0) ohm output impedance of amplifier 102 and 50 ohm characteristic impedance of cable 106, microprocessor 20 controls motors 118 and 120 so the impedance seen looking from cable 106 into matching network 108 is as close as possible to (50+j0) ohms.
To control motors 118 and 120 to maintain a matched condition for the impedance seen looking into the output terminals of amplifier 132 and the impedance amplifier 132 drives, microprocessor 20 responds to signals from conventional sensor arrangement 104 indicative of the impedance seen looking from cable 106 into matching network 108. Alternatively, sensors can be provided for deriving signals indicative of the power that amplifier 102 supplies to its output terminals and the power reflected by matching network 108 back to cable 106. Typically, sensor arrangement 104 includes detectors for current and voltage magnitude and for the phase angle between the current and voltage. Microprocessor 20 responds, in one of several known manners, to the sensed signals that sensor arrangement 104 derives to control motors 118 and 120 to attain the matched condition.
Circuit 14 for supplying RF bias to workpiece 54 via electrode 56 has a construction somewhat similar to circuit 12. Circuit 14 includes constant frequency RF source 130, having a constant output power. The output of source 130 drives electronically controlled variable gain power amplifier 132, having substantially the same characteristics as amplifier 102. The output power of amplifier 32 controls the energy of plasma in proximity to workpiece 54, as disclosed by Patrick et al., U.S. Pat. No. 6,174,450. Amplifier 132 drives a cascaded arrangement including directional coupler 134, cable 136 and matching network 138. Matching network 138 includes a series leg comprising the series combination of fixed inductor 140 and variable capacitor 142, as well as a shunt leg including fixed inductor 144 and variable capacitor 146. Motors 148 and 150, which are preferably step motors, respectively vary the values of capacitors 142 and 146 in response to signals from microprocessor 20.
Output terminal 152 of matching network 138 supplies an RF bias voltage to electrode 56 by way of series coupling capacitor 154 which isolates matching network 138 from the chucking voltage of DC source 66. The RF energy that circuit 14 applies to electrode 56 is capacitively coupled via dielectric layer 48, workpiece 54 and a plasma sheath between the workpiece and plasma to the portion of plasma 50 in close proximity with chuck 52. The RF energy that chuck 52 couples to plasma 50 establishes a DC bias in the plasma; the DC bias typically has values between 50 and 1000 volts. The DC bias resulting from the RF energy circuit 14 applies to electrode 52 accelerates ions in plasma 50 to workpiece 54. If electrode 56 has a bipolar configuration, the plural mutually-insulated metal elements are driven in parallel by output terminal 152 of matching network 138 and appropriate blocking capacitors are provided so there is DC isolation between the metal elements.
Alternatively, RF source 130 is a source arrangement having two or more sources, operating at different frequencies, such as 4.0 MHz, 13.56 MHz and 27.1 MHz. Source 130 simultaneously supplies these different frequencies through different power amplifiers, directional couplers, cables, sensors and matching networks to electrode 56. The lower frequencies cause ion energy in the plasma in proximity to workpiece 54 to increase, while the higher frequencies cause an increase in ion density of the plasma in proximity to workpiece 54.
Microprocessor 20 responds to signals indicative of the impedance seen looking from cable 136 into matching network 138, as derived by known sensor arrangement 139, to control motors 148 and 150 and the values of capacitors 142 and 146 in a manner similar to that described supra with regard to control of capacitors 112 and 116 of matching network 108.
For each process recipe step, memory system 24 stores set point signals for the net power coupled by directional coupler 134 to cable 136. The net power coupled by directional coupler 134 to cable 136 equals the output power of amplifier 132 minus the power reflected from the load and matching network 138 back through cable 136 to the terminals of directional coupler 134 connected to cable 136. Memory system 24 supplies the net power set point signal associated with circuit 14 to microprocessor 20. Microprocessor 20 also responds to output signals directional coupler 134 supplies to power sensor arrangement 141. Sensor arrangement 141 derives signals indicative of output power of amplifier 132 and power reflected by cable 136 back toward the output terminals of amplifier 132.
Microprocessor 20 responds to the set points and measured signals sensor arrangement 141 derives, which measured signals are indicative of the output power of amplifier 132 and the power reflected back to amplifier 132, to control the power gain of amplifier 132 and the plasma energy. The output power of amplifier 132 is also dynamically changed as a function of time as changes in a recipe are ordered by memory system 24. The dynamic changes in the output power are stored in memory system 24 and control the power gain of amplifier 132.
One of the elements of memory system 24, typically read-only memory 30, stores preprogrammed values for controlling the output power of amplifier 102 and/or 132 during a step of the recipe of plasma 50 processing workpiece 54. The preprogrammed values thereby control the amount of power that coil 48 and/or electrode 56 supply to the plasma 50 in chamber 40 to enable the power that coil 48 and/or electrode 56 supplies to the plasma to change as a function of time in accordance with a preprogrammed predetermined function.
A problem with the prior art processors is that ions in the plasma in proximity to workpiece 54 have differing energies and densities at different localized portions of the workpiece. In addition, there are frequently temperature variations at different localized portions of the workpiece. Consequently, when the prior art processors are used for etching purposes, different portions of workpiece 54 are itched differentially and when the processors are used for deposition purposes different amounts of materials are deposited on different portions of the workpiece. While considerable improvement has been made in reducing the differential variations of the processing at different localized portions of the workpiece, problems still remain.
I am aware that Dhindsa, U.S. Pat. No. 5,740,016, discloses an arrangement wherein a workpiece in a plasma processing chamber deals with the problem of different localized portions of the workpiece having different temperatures. The '016 patent deals with the problem by providing a plurality of thermoelectric modules of the Peltier effect type in heat transfer contact with a workpiece holder in the vacuum processing chamber. A current supply interface, connected to the plurality of thermoelectric modules, applies controlled currents to the modules to control the temperature of the workpiece holder and to provide a desired temperature distribution across the workpiece during workpiece processing. The '016 patent assumes that different portions of the workpiece always have the same relative temperature distribution. A controller stores signals indicative of the relative temperature distribution of the different workpiece portions. A single sensor for the entire workpiece temperature controls the level of the signals the controller supplies to the thermoelectric modules. Hence, if the assumption that different portions of the workpiece always have the same relative temperature distribution is not accurate for a particular situation, the approach the '016 patent discloses may not provide optimum temperature control of the workpiece.
It is, accordingly, an object of the present intention to provide a new and improved plasma processor and method of operating same.
Another object of the invention is to provide a new and improved plasma processor apparatus for and method of providing greater uniformity of ion energy and/or ion density of a plasma coupled to a workpiece being processed.
An additional object of the invention is to provide a new and improved electrode arrangement for a plasma processor which enables workpieces to be processed in such a manner that there is greater uniformity of ion energy and/or ion density of plasma coupled to a workpiece being processed.
A further object of the invention is to provide a new and improved plasma processor apparatus for and method of monitoring and controlling localized temperature dependence of a workpiece being processed.
Still an additional object of the invention is to provide a new and improved plasma processor apparatus for and method of providing greater uniformity of ion energy and/or ion density of a plasma coupled to a workpiece being processed, while providing greater temperature uniformity of the processed workpiece.
Yet a further object of the invention is to provide a new and improved electrode arrangement for a plasma processor which enables workpieces to be processed in such a manner that there is greater temperature uniformity of the processed workpiece.
Still an added object of the invention is to provide a new and improved electrode arrangement for a plasma processor, which electrode arrangement enables greater uniformity of ion energy and/or ion density of a plasma coupled to a workpiece being processed, while providing greater temperature uniformity of the processed workpiece.
An added object of the invention is to provide a new and improved plasma processor apparatus for and method of positioning a workpiece on a workpiece holder without using dedicated position transducers.